linux-kernel - Re: futex() on vdso makes process unkillable

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Date:	Tue, 26 Jan 2010 09:33:11 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
cc:	Darren Hart <dvhltc@...ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Mark Seaborn <mrs@...hic-beasts.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	"hugh.dickins" <hugh.dickins@...cali.co.uk>
Subject: Re: futex() on vdso makes process unkillable

On Tue, 26 Jan 2010, KOSAKI Motohiro wrote:
> > Peter Zijlstra wrote:
> > I like the creating-a-real-file solution. However, for now (and for 
> > stable), I think Kosaki's suggestion of EINVAL or EFAULT is a good 
> > stop-gap. EINVAL might play the best with existing glibc implementations.
> 
> May I confirm your mention?
> 
> If we can accept EFAULT, we don't need any change. my previous futex patch
> already did. because 1) VDSO is alwasys read-only mapped 2) write mode
> get_user_pages_fast() against read-only pte/vma return EFAULT.
> 
> Current linus and stable tree don't cause Mark's original problem. instead, just
> return EFAULT. (Well, I'm sorry. my previous mail was unclear. I wrote v2.6.31 test
> result)
> 
> If you can't accept EFAULT, we need to add vdso specific logic into get_futex_key().

EFAULT is perfectly fine. No need for any special tricks.

Thanks,

	tglx

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